1. Field of the Invention
The present invention relates to a printing method and printing apparatus, and more particularly, to a printing method and printing apparatus in which an image is printed on a sheet of paper without top and bottom margins.
2. Description of the Related Art
Generally, a thermal transfer printer has a thermal printing head having a heating element, and a film-shaped ribbon coated with ink. Such a thermal transfer printer is constructed to have a transfer structure in which the ribbon is placed between a sheet of paper and the thermal printing head, and thus, ink sublimed in a predetermined pattern by the thermal printing head is shifted onto the sheet of paper. For full color, a color thermal transfer printer is designed to repeatedly print color-separated yellow, magenta and cyan images superimposed on one another.
In such a printer using an ink ribbon on which sublimation ink dyes of three (or four) colors such as yellow, magenta and cyan (and black) are sheet-sequentially coated, the leading edges of respective color portions must be sought for every revolution of a drum according to a printing signal so that the initial printing position of a sheet of paper coincides with the leading edges of respective color portions.
FIG. 1 shows important components of a conventional thermal transfer printer. A paper feeding cassette 6 is placed on one side under a drum 2. Guide rollers 3 guide paper sheet 4 supplied from paper feeding cassette 6 into contact with the drum and are provided around the circumference of drum 2. A clamp 5, for clamping the leading edge of paper sheet 4 and thereby conveying the paper sheet around drum 2, is provided on a drum shaft 2'. A thermal printing head 1 is installed above drum 2 and is capable of vertical movement (i.e., up and down). An ink ribbon 7 is placed between thermal printing head 1 and paper sheet 4 so that ink is sublimed due to the heat and pressure of thermal printing head 1, thereby causing an image to be printed on paper sheet 4.
In the printing method for the conventional thermal transfer printer discussed as above, first, paper sheet 4 is carried to drum 2 from cassette 6. When paper sheet 4 arrives beneath drum 2, clamp 5 clamps the leading edge of paper sheet 4. Subsequently, as clamp 5 and drum 2 rotate, the leading edge of paper sheet 4 is conveyed to a point slightly beyond thermal printing head 1 as shown in FIG. 1. Then, thermal printing head 1 is lowered to press/heat ink ribbon 7 so that ink is sublimed and thereby an image is printed on paper sheet 4.
In such a conventional thermal transfer printer, however, since paper sheet 4 is carried with the leading edge thereof being clamped by clamp 5, an image cannot be printed over the interval between clamp 5 and the initial printing position 10, that is, the distance "a" from the leading edge of paper sheet 4 (see FIGS. 1 and 2) because such printing would cause clamp 5 and printing head 1 to interfere with one another. This leaves a margin around a printed image, especially on the leading edge portion of paper sheet 4, resulting in a poor appearance and wasted paper.